The disclosure relates to a hydraulic two-way valve according to the description below.
The hydraulic lifting mechanism of an agricultural vehicle is disclosed in U.S. Pat. No. 6,971,453 B2, with reference to FIGS. 1 and 2 therein. The lifting mechanism comprises two hydraulic cylinders 12; 14 for lifting and lowering the lifting mechanism. Said hydraulic cylinders are connected to the first and to the second working connection of a hydraulic two-way valve 24. The two-way valve, moreover, has a pump connection which is connected to a hydraulic pump which is able to deliver hydraulic fluid from a storage tank 18 to the hydraulic cylinders. The two-way valve also has a tank connection which is connected to the storage tank.
The hydraulic two-way valve is configured as a proportional valve and has four switching positions. In the first switching position, the pump connection, the tank connection and the first and the second working connection are shut off, so that the position of the lifting mechanism is not able to be altered.
In the second switching position, the pump connection is connected to the first working connection and the tank connection is connected to the second working connection, so that the lifting mechanism is lowered, wherein the tool connected thereto is able to be pressed against the ground.
In the third switching position, the pump connection is connected to the second working connection and the tank connection is connected to the first working connection, so that the lifting mechanism may be lifted.
Furthermore, a fourth switching position is provided which is configured as a release position, i.e. the first and the second working connections are connected to the tank connection, wherein the pump connection is shut off. In this switching position, the lifting mechanism may be freely lifted and lowered by forces acting from the outside. Said switching position is used when a tool is attached to the lifting mechanism, said tool being supported on the ground when the agricultural vehicle moves, wherein the tool is intended to follow said vehicle. The tool may, for example, be a mowing device.
Moreover, a separate switching valve 42 is provided in U.S. Pat. No. 6,971,453 B2, with which a further switching state is implemented in which the first working connection is connected to the storage tank. Said switching valve is shut off in the already-described switching positions of the two-way valve. In the aforementioned further switching state it is open, wherein the two-way valve is located in the second switching position. The hydraulic pump thus delivers fluid at no load into the tank, so that no pressure builds up on the hydraulic cylinder. In this switching state, the lifting mechanism is only able to be lowered by the intrinsic weight of the attached tool. Said switching state is, for example, used in order to lower the lifting mechanism before it is moved into the release position already discussed.